Antibacterial Residues in Milk and Associated Farm Practices in Peri-urban Sentinel Dairy Farms in Mukono District, Uganda

The presence of antibacterial residues in milk undermines food safety and public health through allergic reactions, disruption of gut microbiota and antimicrobial resistance. A biphasic longitudinal study assessed farm practices influencing antibacterial residues in milk from farms in Mukono district, Uganda. In phase one, 184 samples were collected from 33 dairy farms and assessed for Escherichia coli, Salmonella and Campylobacter jejuni. At least one organism was isolated from 16 farms. The isolated organisms showed antimicrobial resistance to major antibacterial agents. In phase two, the 16 sentinel dairy farms were assessed for antibacterial residues against farm practices such as farm ownership, herd size, antibacterial withdrawal periods and number of lactating cows. Data were collected using participatory observation and a structured questionnaire. Fifty-five (n = 55) composite milk samples were collected from all lactating cows on the study farms and analyzed for residues of sulphonamides, tetracyclines, macrolides, and β-lactams using the CHARM-EZ (Charm QUAD1) test. Antibacterial residues were detected above MRLs with tetracyclines being most prevalent (58%), followed by macrolides (36%) and β-lactams (18%). Treatment duration and personnel administering significantly influenced tetracycline residue occurrence (p = 0.031) and (p = 0.007) respectively. Route of administration was significantly associated with residues- Sulphur (p = 0.000), macrolides (p = 0.000), tetracyclines (p = 0.000), and β-lactams (p = 0.01); oral and topical routes were more strongly associated with residues than parenteral administration. The results indicate irrational use of antibacterial agents in the study area. A larger study should be undertaken to identify other variables contributing towards antibacterial residues in milk.